The present invention relates to a method for producing a narrow molecular weight distribution polyalkylene glycol derivative having an amino group at an end.
Recently, in the drug delivery system, a method for encapsulating drugs in a polymer micelle using a block copolymer formed from a hydrophilic segment and a hydrophobic segment has been proposed (refer to, for example, Japanese Patent No. 2690276, Japanese Patent No. 2777530, and Japanese Patent Application Laid-Open Application No. 11-335267). By using the method, the polymer micelle functions as a carrier of drugs, producing various effects including sustained release in vivo and concentrated dosage to an affected region.
As the hydrophilic segment, many examples with use of a polyalkylene glycol skeleton are proposed (refer to, for example, Japanese Patent No. 2690276, Japanese Patent No. 2777530, and Japanese Patent Application Laid-Open No. 11-335267). A compound having a polyalkylene glycol skeleton has low toxicity in vivo, and enables excretion in kidney to be delayed. Consequently, in comparison with a compound having no polyalkylene glycol skeleton, the retention time in blood can be prolonged. As a result, with use of a drug micellized with a polyalkylene glycol derivative, the dosage amount or dosage frequency can be reduced.
Among polyalkylene glycol derivatives, a compound having an amino group at an end can lead to a block copolymer composed of a polyalkylene glycol skeleton and an amino acid skeleton through a ring-opening polymerization reaction with α-amino acid-N-carboxyanhydride. Many examples with use of the produced block copolymer for encapsulating drugs in a polymer micelle are proposed (refer to, for example, Japanese Patent No. 2690276, Japanese Patent No. 2777530, and Japanese Patent Application Laid-Open Application No. 11-335267).
Synthesis methods of such polyalkylene glycol derivatives having an amino group at an end are also known (refer to, for example, Japanese Patent No. 3050228 and Japanese Patent No. 3562000). In these methods, after polymerization of alkylene oxide with use of a metal salt of monohydric alcohol as a polymerization initiator, a polymer end is converted to a hydroxyl group, and then to a 2-cyanoethoxy group, finally leading to an amino group-containing substituent group (3-amino-1-propoxy group) through hydrogen reduction of the cyano group.
A polymerization example of ethylene oxide in diglyme with use of a potassium salt of substituted diethylene glycol is known, in which the necessary reaction temperature is specified to be 80 to 140° C. with use of diethylene glycol monomethyl ether as co-solvent (with reference to, for example, Japanese Patent No. 4987719).